Gadolinium chloride hexahydrate and its intercalation into synthetic saponite: structure, characterization and slow magnetic relaxation of the intercalated sample

Abstract

The intercalation of [Gd(H2O)6Cl2]+ cation into the synthetic saponite (Sap) was investigated, via direct exchange of the sodium ions by the complex cation along with chloride anions. The final intercalated sample (Gd-Sap) was characterized by powder X-ray diffraction, thermogravimetric analysis, and also, for the first time, by magnetic measurements. Results reveal that throughout the intercalation procedure, the chlorido ligands surrounding the Gd(III) central atom were unbound from its coordination sphere and combined with Na+ cations in the solution. Furthermore, significant increase of the d001 value of the intercalated saponite and its EDX spectra confirmed the presence of the hydrated Gd3+ ions in Sap interlayers. The thermal stability of the intercalated sample containing Gd3+ ions was lower than that of the initial [Gd(H2O)6Cl2]Cl complex (1). DC and AC magnetic study of the Gd-Sap sample revealed slow magnetic relaxation with two relaxation channels. The X-ray single crystal structure analysis of 1 was conducted at two temperatures (173 and 293 K) and confirmed its ionic character. The Gd(III) central atom exhibited slightly deformed square antiprismatic coordination with O6Cl2 donor set. The formation of the supramolecular assembly is controlled by hydrogen bonds of the O-H•••Cl nature. The investigation of static magnetic response is consistent with that for S = 7/2 Heisenberg magnet with small single-ion anisotropy and weak antiferromagnetic magnetic coupling. Magnetic relaxation is found to be mediated by a combination of two relaxation processes. The slow process is determined by transitions among various energy levels in a multilevel spin system induced by lattice degrees of freedom, whereas the fast process is tentatively ascribed to phonon bottleneck effect.